1. Field of the Invention
This invention relates to pixel arrays used for precise detection purposes such as tracing the paths of sub-atomic particles, and to methods and systems for efficiently processing the large amounts of data resident in such arrays.
2. Description of the Related Art
There is a need for pixel detection systems capable of handling enormous amounts of data. In particular, work is currently progressing on a Superconducting Super Collider (SSC) used to generate and analyze sub-atomic particles. In the SSC, contradirected beams consisting of packets of atomic particles are collided with each other. Most of the particles pass through the other packet without encountering a collision, but some of the particles travelling in opposite directions will collide and generate sub-atomic particles. These particles in turn may disintegrate into additional particles. The locations of particle collisions are referred to as primary vertices, while the locations where sub-atomic particles generated through such collisions disintegrate into further particles are referred to as secondary vertices. The process takes place at a very fast rate, with successive particle packets arriving at the collision area at intervals of about 16 nanoseconds.
Arrays of silicon strip detectors are currently positioned in the area where collisions take place, and used in an effort to trace the vertex locations based upon the pattern of strip detectors that are hit by sub-atomic particles. However, strip detectors are fairly long devices, on the order of 1 cm, and any attempt to resolve with precision where a particle has hit them requires a large amount of computer time and power. In an attempt to limit the amount of data required to be processed, a "sparse" data processing technique has been developed that processes data only from the strip detectors that have actually been hit by sub-atomic particles, ignoring the remainder. Such an approach is discussed in Spieler, "Integrated Microsystems as a Driving Force in Modern Detector Designs", International Conference on the Impact of Digital Microelectronics and Microprocessors on Particle Physics, Trieste, Italy, Mar. 28-30, 1988. A silicon strip vertex detector is described in which the detector channels are automatically scanned for particle hits; information is processed only from the strip detectors that have received hits. While this significantly reduces the amount of data to be processed, the resolution is still not very high, and the requirement for continuous scanning is not well matched to the SSC environment.
A significantly higher vertex resolution could be achieved by using arrays of small scale pixels, rather than the relatively long strip detectors, to detect the sub-atomic particles traveling away from the vertices. Such a system, however, would require something on the order of 10.sup.8 pixels per vertex detector. Analog information describing the charges generated by the particle hits at each detector, not just digital information on whether or not a particular pixel has been hit, would be required, and it would be desirable to provide the analog data with six bit accuracy. Thus, something on the order of 6.times.10.sup.8 bits of data would be generated every 16 nanoseconds, for a data rate of about 10.sup.16 -10.sup.17 bits per second. This is considerably beyond the capacity of present systems to handle.